Among vehicular lamps are turn signal lamps (hereinafter referred to as turn lamps) for notifying nearby drivers etc. of an upcoming left or right turn of the self vehicle. And turn signal lamps include ones using plural light sources such as LEDs (light-emitting diodes).
For example, JP-A-2015-81000 discloses a configuration in which plural systems of LED groups are connected to each other in parallel. JP-A-2015-145224 discloses a sequential lighting type turn lamp in which plural light source are turned on sequentially.
Incidentally, for vehicular lamps to be permitted use in a certain country, their lighting operation is required to satisfy various related laws of that country. For example, to satisfy the related laws established in North America, a turn lamp should be turned off as a whole even when only part of its plural light sources have suffered a disconnection failure. To this end, it is necessary to employ a configuration that ensures execution of a necessary control by detecting a disconnection in each light source before turning-on of a turn lamp. However, this raises a problem that a control circuit is made complex and increased in size and cost.
To perform sequential lighting using plural light sources in a turn lamp, disconnections of part of the light sources an event that a sequential lighting operation is terminated halfway or the part of the light sources do not light. Such an imperfect sequential lighting operation looks poor and lowers the product value and may disable the turn signal function. Thus, it is desirable to turn off the turn lamp as a whole even when only part of the light sources have suffered a disconnection failure. However, as in the above-described case, this raises a problem that a control circuit is made complex and increased in size and cost.